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Abstract:

The present invention relates to a hydrostatic transmission closed
circuit comprising
a fluid tank (50),
a hydraulic pump (12; 212),
a first engine assembly (20; 220) and a second engine assembly (30, 40;
230), said first and second engine assemblies (30, 40; 230), each
comprising at least one hydraulic engine,
a booster pump (14; 214),
an exchange unit (60; 260),
said circuit being characterised in that it also comprises a
supplementary boosting line (150; 350) which removes fluid at the outlet
of the exchange unit (60; 260) and boosts the hydrostatic transmission
circuit at the level of the series line (104; 204).

Claims:

1. A hydrostatic transmission closed circuit, comprising a fluid tank
(50), a hydraulic pump (12; 212), a first engine assembly (20; 220) and a
second engine assembly (30, 40; 230), said first and second engine
assemblies (30, 40; 230), each comprising at least one hydraulic engine,
said first engine assembly (20; 220) being connected to the hydraulic
pump (12; 212) by a supply line (102; 202), and being mounted in series
with said second engine assembly (30, 40; 230) via a series line (104;
204), said second engine assembly (30, 40; 230) being connected to the
hydraulic pump (12; 212) by a return line (106; 206), a booster pump (14;
214) which removes fluid in the fluid tank (50) and boosts the closed
circuit at the level of the series line (104; 204), an exchange unit (60;
260) connected to the closed circuit, and which extracts therefrom a
volume of fluid injected by the booster pump (14; 214), said circuit
being characterised in that it also comprises a supplementary boosting
line (150; 350) which removes fluid at the outlet of the exchange unit
(60; 260) and boosts the hydrostatic transmission circuit at the level of
the series line (104; 204).

2. The hydrostatic transmission circuit as claimed in claim 1, in which
the supplementary boosting line comprises a check valve adapted so that
fluid can flow only in the direction of the supplementary boosting line
to the series line.

3. The hydrostatic transmission circuit as claimed in any one of the
preceding claims, characterised in that the first engine assembly
comprises two elementary hydraulic engines on the same transmission
shaft, the first of these two elementary engines being connected to the
hydraulic pump by the return line, and. the second of these two
elementary engines being connected. by the series line to the second
engine assembly.

4. The hydrostatic transmission circuit as claimed 11 any one of the
preceding claims, characterised in that said second engine assembly
comprises two hydraulic engines mounted in parallel relative to one
another.

5. The hydrostatic transmission circuit as claimed in any one of the
preceding claims, characterised in that said exchange unit comprises an
exchange spool and a valve in series, said boosting line being connected
to the exchange unit at a point located between said slide valve and said
valve.

6. The hydrostatic transmission circuit as claimed in the preceding
claim, characterised in that: said exchange unit comprises two inlets and
an outlet, said exchange spool comprises two inlets and an outlet, said
valve of said exchange unit comprises an inlet and an outlet, said two
inlets of the exchange unit being connected to the two inlets of the
exchange spool, an outlet of the exchange spool being connected to the
inlet of the valve of the exchange unit, an outlet of the valve of the
exchange unit being connected to the outlet of the exchange unit.

7. The hydrostatic transmission circuit as claimed in the preceding
claim, characterised in that: the first inlet of the exchange unit is
connected to the supply line on the one hand, and to the first inlet of
the exchange spool on the other, the second inlet of the exchange unit is
connected to the return line on the one hand, and to the second inlet of
the exchange spool on the other, said exchange spool comprising three
positions: a first position in which the first inlet of the exchange
spool is closed, and the second inlet of the exchange spool is connected
to the outlet of the exchange spool, a second position in which the first
inlet of the exchange spool, the second inlet of the exchange spool, and
the outlet of the exchange spool are closed, a third position in which
the first inlet of the exchange spool is connected to the outlet of the
exchange spool, and the second inlet of the exchange spool is closed.

8. The hydrostatic transmission circuit as claimed in any one of the
preceding claims, characterised in that said engines are hydraulic
engines with radial pistons and multilobe cams

Description:

GENERAL TECHNICAL FIELD

[0001] The invention relates to the field of hydrostatic transmission
circuits, in particular for industrial machines or industrial vehicles.

[0002] More precisely, the present invention relates to the field of
circuits designed to supply hydraulic engines.

PRIOR ART

[0003]FIG. 1 presents a hydrostatic transmission closed circuit according
to the prior art, typically used for industrial machines or engines such
as construction, agricultural or heavy weight-handling engines.

[0004] The closed circuit presented in FIG. 1 comprises a pump module 10,
a first hydraulic engine unit 20, a second hydraulic engine unit 30, a
third hydraulic engine unit 40, a fluid tank 50, and an exchange unit 60.

[0007] In the embodiment illustrated, the first engine unit 20 comprises
two hydraulic engines 22 and 24 mounted in parallel, and designated
respectively hereinbelow as first 22 and second 24 elementary engine of
the first engine unit 20, these two elementary engines 22 and 24 being
located on the same transmission shaft.

[0010] Each of the hydraulic engines, elementary engines and pumps
comprises two connections, which can be used at inlet or outlet according
to the operating mode.

[0011] The hydraulic pump 12 is connected by its first connection 12.1 to
the first engine unit 20 by a supply line 102, and feeds the two
elementary engines 22 and 24 of the first engine unit 20 via their first
connections, respectively 22.1 and 24.1. The first elementary engine 22
is then connected via its second connection 22.2 to a return line 106,
which is connected to the second connection 12.2 of the hydraulic pump
12.

[0012] A series line 104 then connects the second connection 24.2 of the
second elementary engine 24 of the first engine unit 20 to each of the
first connections, respectively 32.1 and 42.1 of the second engine 32 and
of the third engine 42. These two engines 32 and 42 each mounted directly
in series with the second elementary engine 24 of the first engine unit
20 are mounted in parallel to each other.

[0013] The second engine 32 and the third engine 42 are then connected to
the hydraulic pump 12 via the return line 106 which is connected to their
second connections, respectively 32.2 and 42.2.

[0014] According to a particular embodiment, the engines are connected
according to a link called Twin-Lock, such as known from the prior art,
for combining the advantages of links of parallel and series type for
hydraulic engines. In fact, conventionally, hydraulic engines are mounted
in series or in parallel, these two types of mounting having distinct
advantages and disadvantages.

[0015] A series link between two hydraulic engines turns these two engines
at the same speed if their cylinders are identical, but has disadvantages
with respect to distribution of torque, which is limited to the torque of
the first of said engines en the series line, and has no different
rotation speeds, especially in turns.

[0016] A parallel link between two hydraulic engines has as such different
engine rotation speeds, but offers disadvantages in terms of skidding;
torque is limited to the lowest torque value of the two hydraulic
engines.

[0017] The housings of the engines 22, 24, 32 and 42 are connected to a
leakage line 108, for conveying fluid losses in these engines to the
fluid tank 50. Such a leakage line is typically connected to the engine
housings, in which fluid losses are collected.

[0018] The exchange unit 60 comprises two inlets and an outlet, the two
inlets being connected respectively to the supply line 102 and to the
return line 106, and the outlet being connected to an exchange line 66.

[0019] In the embodiment illustrated, the exchange unit 60 comprises an
exchange spool 62 and a valve 64 mounted in series.

[0020] The exchange spool 62 comprises two inlets and an outlet, and the
valve 64 comprises an inlet and an outlet. The two inlets of the exchange
spool 62 are connected to the two inlets of the exchange unit 60, and its
outlet is connected to the inlet of the valve 64, the valve 64 being
connected at the other end by its outlet to the outlet of the exchange
unit 60.

[0021] The exchange spool 62 comprises three positions for defining the
links between two inlet paths and one outlet path, the position employed
being defined by the difference in pressure in the two inlet paths.

[0022] In the embodiment illustrated in FIG. 1, the exchange unit 60 is
adapted for removing fluid in the line having the lowest pressure between
the supply line 102 and the return line 106 so as not to penalise the
transmission output.

[0023] The exchange spool 64 as such has a pressure limitation function,
at a. level slightly less than that of the booster valve 128.

[0024] More generally, the exchange unit 60 produces a fluid outlet, and
can for example comprise leak jets, or any other means adapted to remove
fluid from the closed circuit.

[0025] Removing fluid in this way from the closed circuit refreshes the
fluid which is circulating, the fluid outlets by the exchange unit 60
being compensated by the booster pump 14 which reinjects fluid removed to
the fluid tank 50.

[0026] In the embodiment illustrated, the fluid originating from the
exchange unit 60 is injected into the pump module 10, for example in a
housing of this pump module 10, prior to being cooled by fluid-cooling
means 52 then reinjected into the fluid tank 50.

[0027] In the event of excess pressure in the exchange line 66, a bypass
line 68 directly injects the fluid from the exchange line 66 into the
fluid tank 50 via a check valve 69 acting as pressure limiter.

[0028] The booster pump 14 boosts the hydrostatic transmission circuit at
the level of the series line 104, and in the line having the lowest
pressure of the supply line 102 and the return line 106.

[0029] The booster pump 14 is connected to a boosting line 120 via its
first connection 14.1, said boosting line 120 connecting the booster pump
to the supply line 102, the series line 104 and the return line 106 via
check valves, respectively 122, 124 and 126.

[0030] The supply line 102, the series line 104 and the return line 106
are likewise connected to the boosting line 120 via valves limiting the
pressure in these lines, respectively 132, 134 and 136.

[0031] A brake circuit 140 passes via the boosting line 120, and actuates
a brake 142 of the first engine unit 20 when a brake command 144 is
actuated.

[0032] This brake command conveys fluid from the boosting line 120 to the
brake 142, which then acts on the first engine unit 20. This system
functions by anti-skid, that is, the brake is applied when there is no
pressure in the line 140, resulting automatically in braking of the
machine when the pump module is stopped.

[0033] The booster pump 14 is likewise used by the control means of the
position of the wobble plate of the variable-flow pump 12. These means
are internal to the pump module 10 and are not shown.

[0034] The booster pump 14 is fed with fluid by way of an inlet line 15
connected to the second connection 14.2 of the booster pump 14, which
connects the booster pump 14 to the fluid tank 50.

[0035] In the event of excess pressure in the boosting line 120, a valve
128 removes fluid from this boosting line, typically by sending it back
to the tank 50 (Even though there are several small tanks shown in the
figures, this is a single tank.), either via the line 52, or via 68 and
69.

[0036] By way of a feed pump 12, this circuit supplies three engine units
20, 30 and 40 with fluid, here mounted according to Twin-Lock technology.
A booster pump 14 supplies a boosting line 120, which ensures adequate
fluid pressure in the circuit, and compensates losses by injecting into
the circuit fluid removed in a fluid tank 50, and likewise ensures the
rate of exchange via the unit 60. (a conduit not numbered starting from
the booster pump 14, passing through the valves 122 and 126, the line 106
or 102, the exchange unit 60). For this to happen, the valve 128 is
calibrated at a level of pressure greater than the valve 64.

[0037] This circuit does have disadvantages in some operating modes. In
fact, boosting can prove inadequate during turns, or when the machine
goes lowly and the thermal drive engine of the pump idles. The drop in
boosting pressure which ensues can cause inopportune application of the
brakes 142, and likewise perturb control of the flow-control wobble plate
of the hydraulic variable-flow pump 12. These organs can no longer ensure
their functions at preferred levels of performance and cause vibrations
and aftershocks on the machine.

[0038] A conventional method for responding to these disadvantages
consists of using a booster pump of superior capacity; but this causes an
increase in the bulk of the circuit as well as the cost of the circuit,
due to the cost of the pump itself, and to its higher operating cost.

[0042] a first engine assembly and a second engine assembly, said first
and second engine assemblies, each comprising at least one hydraulic
engine, said first engine assembly being connected to the hydraulic pump
by a supply line, and being mounted in series with said second engine
assembly via a series line, said second engine assembly being connected
to the hydraulic pump by a return line,

[0043] a booster pump which removes fluid in the fluid tank and boosts the
closed circuit at the level of the series line,

[0044] an exchange unit connected to the closed circuit, and which
extracts therefrom a volume of fluid injected by the booster
supplementary pump, said circuit being characterized in that it also
comprises a boosting line which removes fluid at the outlet of the
exchange unit and boosts the hydrostatic transmission circuit at the
level of the series line.

[0045] According to a particular embodiment, the supplementary boosting
line comprises a check valve adapted so that fluid can flow only in the
direction of the supplementary boosting line to the series line.

[0046] According to another particular embodiment, the first engine
assembly comprises two hydraulic elementary engines on the same
transmission shaft, the first of these two elementary engines being
connected to the hydraulic pump by the return line, and the second of
these two elementary engines being connected by the series line to the
second engine assembly.

[0047] According to a particular embodiment, the second engine assembly
comprises two hydraulic engines mounted in parallel relative to one
another.

[0048] According to a particular embodiment, the exchange unit comprises
an exchange spool and a valve in series, said boosting line being
connected to the exchange unit at a point located between said slide
valve and said valve.

[0049] According to a variant of this particular embodiment:

[0050] said exchange unit comprises two inlets and an outlet,

[0051] said exchange spool comprises two inlets and an outlet,

[0052] said valve of said exchange unit comprises an inlet and an outlet,
said two inlets of the exchange unit being connected to the two inlets of
the exchange spool,

[0053] an outlet of the exchange spool being connected to the inlet of the
valve of the exchange unit,

[0054] an outlet of the valve of the exchange unit being connected to the
outlet of the exchange unit.

[0055] According to a variant of this particular embodiment:

[0056] the first inlet of the exchange unit is connected to the supply
line on the one hand, and to the first inlet of the exchange spool on the
other,

[0057] the second inlet of the exchange unit is connected to the return
line on the one hand, and to the second inlet of the exchange spool on
the other,

said exchange spool comprising three positions:

[0058] a first position in which the first inlet of the exchange spool is
closed, and the second inlet of the exchange spool is connected to the
outlet of the exchange spool,

[0059] a second position in which the first inlet of the exchange spool,
the second inlet of the exchange spool, and the outlet of the exchange
spool are closed,

[0060] a third position in which the first inlet of the exchange spool is
connected to the outlet of the exchange spool, and the second inlet of
the exchange spool is closed.

[0061] According to another particular embodiment, the engines are radial
piston engines marketed by the company Poclain Hydraulics.

PRESENTATION OF FIGURES

[0062] Other characteristics, aims and advantages of the invention will
emerge from the following description, which is purely illustrative and
non limiting, and which must be considered in conjunction with the
attached diagrams, in which:

[0063]FIG. 1 described previously presents a hydrostatic transmission
circuit according to the prior art.

[0064] FIG. 2 presents a hydrostatic transmission circuit according to the
invention.

[0066] FIG. 2 presents a hydrostatic transmission circuit according to the
invention.

[0067] The circuit illustrated in FIG. 2 comprises a hydraulic pump 212, a
first hydraulic engine 220, a second hydraulic engine 230, and a booster
pump 214.

[0068] Each of the hydraulic engines and pumps comprises two connections
which can be used as inlet or outlet according to the operating mode.

[0069] The hydraulic pump 212 is connected by its first connection 212.1
to a supply line 202 which is likewise connected to the first connection
220.1 of the first hydraulic engine 220.

[0070] The first hydraulic engine 220 is connected by its second
connection 220,2 to a series line 204 which is likewise connected to the
first connection 230.1 of the second hydraulic engine 230.

[0071] The second hydraulic engine 230 is connected by its second
connection 230.2 to a return line which is then connected to the second
connection 212.2 of the pump 212. The booster pump 214 is connected by
its connection 214.1 to a boosting line 320 which is then connected to
the series line 204 to enable boosting of this series line 204.

[0072] The boosting line comprises a check valve 324, as well as a valve
334 for limiting the pressure in the series line 204. The boosting line
is likewise connected to the supply line 202 and to the return line 206,
these links being likewise fitted with check valves, respectively 322 and
326, and valves, respectively 332 and 336.

[0073] A valve 328 limits the pressure in the boosting line 320, and
removes fluid from this boosting line in the event of excessive pressure,
typically by sending this fluid back to a fluid tank.

[0074] The circuit likewise comprises fluid exchange means 260, designed
to remove fluid in the supply line 202 and/or in the return line 206, and
remove fluid removed from the circuit, typically to allow cooling and/or
refreshing of the fluid.

[0075] A supplementary boosting line 350 according to the present
invention is added, and connects the fluid exchange means 260 to the
series line 204.

[0076] This supplementary boosting line 350 is typically fitted with a
check valve 354 to provide circulation of fluid only in the direction of
the supplementary boosting line 350 to the series line 204.

[0077] Such a supplementary boosting line 350 ensures adequate boosting of
the hydraulic control circuit, without requiring the use of an oversized
booster pump, enabling economising at the same time in terms of the
booster pump per se; but likewise in terms of its function and its bulk.

[0078] In addition, this supplementary boosting line 350 requires no
installation of complex or bulky supplementary components in the circuit,
and requires only the addition of a fluid line between two elements.

[0079] The circuit presented in FIG. 2 thus feeds two hydraulic engines
220 and 230 mounted in series, and ensures adequate boosting especially
during turns, or when the machine goes slowly and the engines and pumps
are idling, without the need for oversizing the booster pump 214.

[0080]FIG. 3 presents an application of the invention to the hydrostatic
circuit presented in FIG. 1.

[0081] This FIG. 3 shows elements already described for FIG. 1, these
elements being designated by the same reference numeral as for FIG. 1.
This circuit also comprises a supplementary boosting line 150 such as
presented in FIG. 2, which connects the exchange unit 60 to the series
line 104 via a supplementary check valve 154.

[0082] In the embodiment illustrated, the link point with the
supplementary boosting line 150 is located between the outlet of the
exchange spool 62 and the inlet of the valve 64 of the exchange unit 60.

[0083] This supplementary boosting line 150 thus removes fluid initially
destined to be sent to the exchange line 66, and reinjects it into the
series line 104.

[0084] As mentioned earlier in the description of FIG. 1, the fluid
passing through the exchange unit 60 originates from the line having the
lowest pressure of the supply line 102 and the return line 106 so as not
to penalise the motor control of the engines.

[0085] In the embodiment represented in FIG. 3, the supplementary boosting
line 150 comprises a supplementary check valve 154, adapted so that fluid
can flow only in the direction of the supplementary boosting line 150 to
the series line 104.

[0086] Having the supplementary boosting line takes advantage of existing
components which are likely to comprise connections not used by
conventional components of the circuit, and which can thus be exploited
for adding this supplementary boosting line 150.

[0087] More generally, the supplementary boosting line 150 can be
connected to an exchange unit 60 such as represented in the figures, or
at any other element for removing fluid from the closed circuit.

[0088] The invention applies particularly to hydrostatic transmission
circuits in which the engines are hydraulic engines with radial pistons
and multilobe cams, also called high-torque and low-speed engines.